This invention relates to a process for the preparation of benzophenone, anthraquinone and o-dibenzoylbenzene, and their substituted derivatives.
In general, the common methods of synthesis of ketones can be divided into (1) synthesis from acid halides and organometallic compounds, (2) synthesis from carboxylic acids, (3) Friedel-Crafts reactions, and (4) enolate condensations.
Synthesis from acid halides and organometallic compounds has been extensively used but costs of the organometallic reagents are relatively expensive and care must be used in handling. The use of carboxylic acids and their salts for ketone synthesis suffers from the disadvantage that the method will produce in general only the symmetrical ketones in good yields. The Friedel-Crafts acylation reactions generally give good yields. However, their use is restricted by the orientation of the acyl group introduced and the metal halides are expensive with attendant waste disposal problems. Enolate condensations give a variety of products; however, the overall yields are frequently not so good as those that can be obtained by other methods, and procedures frequently are more involved.
As is well-known, the important methods of formation of benzophenone, i.e., benzophenone, and its substituted derivatives are the following: (1) oxidation of diphenylmethanes or benzhydrols, e.g., by chromic acid or by oxygen in presence of a catalyst, for example, as is taught in U.S. Pat. No. 2,859,274; (2) hydrolysis of ketone chlorides; (3) condensation of benzoyl halides with benzene, its homologues, and substituted derivatives having a reactive position, in presence of AlCl.sub.3 or other catalyst, or under high pressure, as taught in U.S. Pat. No. 2,528,789; (4) reaction of a benzonitrile (or benzoyl halide) with a phenylmagnesium halide; (5) distillation of calcium or other suitable benzoate (Ann. 12, 41).
Preparation of anthraquinone specifically has been proposed by several different processes: (1) the Diels-Alder reaction of butadiene on 1,4-naphthoquinone, (2) oxidation of anthracene in the presence of catalysts, (3) Friedel-Crafts reaction with benzene and phthalic anhydride, (4) oxidation of suitable precursors such as indane. In the Friedel-Crafts process, since a large amount of aluminum chloride is necessary, disposal of the wastes from the process is difficult. Furthermore, since isomerization reactions, rearrangement reactions, and elimination reactions occur in the process, many by-products derived from these reactions contaminate the product. Oxidation of anthracene is economically accomplished only when relatively pure anthracene is available at moderate costs. The Diels-Alder reaction suffers from the high cost of naphthoquinone. U.S. Pat. Nos. 2,794,813; 3,699,134; 3,872,134; 3,872,135; 4,002,653; 4,036,860; 4,036,861; and 4,215,063 teach typical processes for manufacture of anthraquinone by oxidation of diphenylmethane compounds. These processes produce many by-products.
o-Dibenzoylbenzene has been reported as most satisfactorily prepared by a reaction carried out by adding phenylmagnesium bromide to a solution of phthaloyl chloride in ether at -55.degree. C. (F. R. Jensen, J. Org. Chem., 25, 269 (1960)). The product forms an ether-insoluble complex with magnesium bromide. Addition of water liberates the o-dibenzoylbenzene. However, the yield of o-dibenzoylbenzene prepared by this complicated method is reported as poor (32%).
As a result of these difficulties, considerable investigations have been carried out in efforts to develop synthesis of benzophenone, anthraquinone and o-dibenzoylbenzene whereby the desired products in good yield are obtained by simple economic methods, without problems of waste disposal. This invention relates to a method for pyrolysis of yttrium, erbium, or dysprosium salts of benzoic acid whereby benzophenone, anthraquinone, and o-dibenzoylbenzene are produced in good yield. The process can be by batch or by continuous method.